Some of the recently developed gasoline and diesel internal combustion engines are fitted with a valve opening property varying mechanism to improve the output and fuel economy of the engine and reduce undesired emissions from the engine. A relatively known form of valve opening property varying mechanism is provided with low speed cams and high speed cams that can be interchangeably used depending on the operating condition of the engine. More recent attempts include those capable of continuously varying the valve opening properties (such as valve lift and valve timing) to further improve the transient response of the engine and to dispense with a throttle valve. See Japanese patent laid open publication No. 2005-291011.
According to a known variable valve opening property engine, a link mechanism is used for varying the valve opening property. In such a case, to prevent uncontrolled movement of the link member, it is desired to keep the link member in contact with an associated member of the valve actuating mechanism such as a cam and a rocker arm by biasing them toward each other by using a spring. In particular, because the relative position of such two members change in response to the varying of the valve opening property, it is necessary that the spring is arranged so as to accommodate such a relative movement.
However, the presence of the link mechanism required for varying the valve opening property necessitates a complication of the valve actuating mechanism, and this imposes a restriction on the positioning of the spring. This in turn prevents the efficient transmission of the spring force to the part where the spring force is needed, Consequently, the spring is required to produce an unduly large spring force in order to provide a required spring force under all conditions.